1. Technical Field of the Invention
The present invention relates to disk drive circuits and, more particularly, to an apparatus, system and method for biasing a pre-amplifier in a disk drive circuit.
2. Description of Related Art
One of the more exciting developments in magnetic recording on hard disk drives in recent years is the development of magneto resistive (MR) sensors or heads. The phenomenon of magneto resistance has been known for a long time. The basic effect is that when a magnetic field is applied to a MR material the resistance of the material changes. Thin film strips of Permalloy exhibit magneto resistivity between two and three percent of the intrinsic resistivity of the material. Because of the accumulated knowledge and significant magneto resistance, a thin film of Permalloy became the material of choice for the research of MR sensors for recording applications.
Conventional magnetic storage devices include a magnetic transducer or head suspended in close proximity to a recording medium; for example, a magnetic disk having a plurality of concentric tracks. The transducer is supported by a flexible to suspension. During normal operation, relative motion is provided between the transducer and the recording medium as an actuator dynamically positions the transducer over the desired track.
Writing data to the recording medium is typically performed by applying a current to a coil of the head so that a magnetic field is induced in an adjacent magnetically permeable core, with the core transmitting a magnetic signal across a spacing of the disk to magnetize a small pattern or digital bit of the media within the disk.
Reading of the information in the disk is performed by sensing the change in magnetic field of the core as the transducer passes over the bits in the disk. The changing magnetic field induces a voltage or current in the inductively coupled coil. Reading of the information can be accomplished by employing a magneto resistive head, which has a resistance that varies as a function of the magnetic field adjacent to the sensor. Connected to these heads are read circuits, such as a reading pre-amplifier, which amplify the recorded data and reduce noise. Assuming that the disk track has previously written data, the following sequence of events converts them into user bits: first, as magnetic poles pass near the head gap, the core of the head becomes magnetized; and second, the change in magnetism in the core results in an electric signal across the head coil. These electric signals are subsequently amplified and after a series of other operational steps results in usable data supplied to a computing processor.
For many years, several important issues related to making MR heads such as different biasing schemes, biasing recovery time, and noise reduction, for example, have been investigated. The pursuit of higher density storage devices has resulted in increased noise. Circuit consideration such as noise reduction capacitors can be utilized to reduce noise and improve the signal-to-noise ratio, however, the noise reduction capacitors also slow the bias recovery time of the circuit.
A problem in current disk storage circuits is the extreme sensitivity to electrical noise. In disk storage circuits, the signal is relatively small, thus, additive electrical noise can make detection of data difficult. To address the problem, noise reduction components, such as capacitors, are utilized to improve the signal-to-noise ratio of the circuits. However, these capacitors can also slow the bias response time and speed of the disk storage device. Therefore, what is needed is a system and method for decreasing the bias response time for those circuits which utilize noise reduction capacitors.
The present invention achieves technical advantages as an apparatus, system and method of decreasing the bias response time for pre-amplifier circuits which utilize noise reduction capacitors. The system uses a quick recovery circuit with an output which is selectively switched to operatively connect to a node of the noise reduction capacitor. The quick recovery circuit is electrically connected in parallel to the noise reduction capacitor and comprises a resistor, an amplifier, and a mirrored current source. The resistor value is selected to closely match the resistance of the reference resistor of the pre-amplifier circuit. The mirrored current source is arranged to closely follow the current adjustments made at the current source of the pre-amplifier circuit. The output of the amplifier serves as a feedback loop and is electrically connected to a reference node of the pre-amplifier circuit.